Safety component in a programmable components chain

ABSTRACT

An electronic circuit includes a plurality of programmable components connected in an electronic chain. An interface is adapted to connect the programmable components to an external controller wherein the controller is adapted to program the programmable components. A component isolation element is connected to the interface at an input end and to the electronic chain of the programmable components at an output end wherein the isolation element is adapted to isolate one component of the programmable components from the electronic chain and wherein the one component is a safety component.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned copending U.S. patent applicationSer. No. ______(Attorney Docket No. K000653US01NAB), filed herewith,entitled METHOD OF PROGRAMMING A SAFETY COMPONENT, by Gez; thedisclosure of which is incorporated herein.

FIELD OF THE INVENTION

This invention relates in general to programming a complex programmablelogic device (CPLD) and in particular to programming a safety electroniccircuit.

BACKGROUND OF THE INVENTION

Computer-to-plate (CTP) imaging devices use laser diodes for imaging ona substrate. Leakage of laser light from the imaging device duringimaging operation may be hazardous to people in proximity to the device.Various safety measures may be required as high power invisible laser(IR) beams are present at least in the optical fibers of the deviceduring operation and could cause eye damage if they leaked from thedevice. Interlock sensors are deployed in the device at variouslocations to notify of hazardous situations or to prevent, for example,opening the device door during operation. The sensors are integratedwith specific electronic circuitry as shown in FIG. 1. When one or moreof the interlock and safety sensors goes off, indicating a potentialleak of laser light, the laser sources are disabled and fault warningactivated.

Safety devices are mandatory in potentially hazardous products, and arerequired to be installed by international safety standards. Safetymeasures in devices can be incorporated by various means such assoftware, electronic CPLD components or electro-mechanical components.In the case of CPLD components, the CPLD components are installed on ancircuit board, which may include more than one CPLD component. One ofthe CPLD components may be used for safety.

CPLD components are programmable and the programming is done via a jointtest action group (JTAG) port residing on the electronic board andconnected typically to a personal computer by an appropriate cable. TheCPLD reprogramming may be done by service engineers in the field,therefore it is essential to prevent reprogramming of the CPLDcomponents related to safety and make sure they are programmed only atthe manufacturing site. Reprogramming of CPLDs which are intended forsafety control in the field is dangerous since it may hinder safeoperation of the product, and thus may cause irreversible harm to theproduct operators, during product operation.

FIG. 1 shows several CPLD components (124, 128, 132) residing onelectronic board 100. The JTAG interface is connected to each of theCPLD components by input and output pins (TDI, TDO) and timing and clockpins (TMS, TCK). The signals TDI, TDO, TMS and TCK are used foraccessing and programming of the CPLDs residing on electronic board 100.The CPLD components are concatenated between each other via the inputand output pins (TDI, TDO). The TDI signal from JTAG interface 108 isconnected to first CPLD 124 via its TDI line. The output line TDO ofCPLD 124 is further connected to the input line TDI of the next CPLD inthe chain 128. The output pin TDO of the last CPLD in the chain 132 isconnected to the TDO line of JTAG interface 108 to form a complete chainof the CPLDs on electronic board 100. The timing TMS and clock pin TCKare connected in parallel from JTAG interface 108 to all CPLDs (124,128, 132) and controlled by timing and clock pins (TMS, TCK).

The programming of the CPLD components is performed by an externalcontroller 104. The programming data is delivered to JTAG interface 108via interface lines 112. The content of each of the CPLD components(124, 128, 132) can be independently programmed by controller 104. CPLD124, which is selected to serve safety measures, has to be treated withmore caution than other CPLDs, therefore programming of CPLD 124 shouldbe permitted only once and at the manufacturing site only. Programmingat a customer site is unacceptable.

SUMMARY OF THE INVENTION

Briefly, according to one aspect of the present invention an electroniccircuit includes a plurality of programmable components connected in anelectronic chain. An interface is adapted to connect the programmablecomponents to an external controller wherein the controller is adaptedto program the programmable components. A component isolation element isconnected to the interface at an input end and to the electronic chainof the programmable components at an output end wherein the isolationelement is adapted to isolate one component of the programmablecomponents from the electronic chain and wherein the one component is asafety component.

The invention and its objects and advantages will become more apparentin the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art schematic showing several concatenated CPLDcomponents;

FIG. 2 is a schematic showing the first CPLD (safety CPLD) concatenatedwith several other CPLD components before programming; and

FIG. 3 is a schematic showing the first CPLD (safety CPLD) concatenatedwith several other CPLD components after programming.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the disclosure.However, it will be understood by those skilled in the art that theteachings of the present disclosure may be practiced without thesespecific details. In other instances, well-known methods, procedures,components and circuits have not been described in detail so as not toobscure the teachings of the present disclosure.

FIG. 2 and FIG. 3 show an electronic board 200. Board 200 is formed witha similar configuration to the prior art shown with board 100 in FIG. 1.The difference between board 100 and board 200 is in that board 200 isequipped with electronic means adapted to isolate CPLD 124 from theother CPLD in CPLDs chain (128, 132).

The isolation of CPLD 124 which is the safety CPLD is achieved byaddition of analog switches 204 and 212. Analog switch 204 switches lineTDI between CPLD 124 and the chain of the other CPLDs (128, 132).Similarly analog switch 212 switches line TDO between CPLD 124 and thechain of the other CPLDs. The isolation of CPLD component 124 whenresiding in board 200 enables CPLD 124 to be limited to singularprogramming, thus prevents any further programming that may negativelyaffect safety conditions of the device.

The CPLD components (124, 128, 132) are not programmed at its originalstate. At the first power up the IO pins are in a logical tri state.FIG. 2 shows a pull down resistor R1 which sets IO pin into logicalstate “0” prior programming 224. At this state analog switch 204connects input pin TDI to OUT1 via switch 208, whereas analog switch 212connects output pin TDO to IN1 via switch 216. Resistor R2 and capacitorC1 act as delay circuit. This setup isolates CPLD 124 for programmingsince TDI and TDO are connected only to CPLD 124 via analog switches 204and 212. Program mode (program done) is represented by line 220.

The next step is to program the safety CPLD 124. Controller 104 programsCPLD 124 via JTAG interface 108. FIG. 3 shows board 300 afterprogramming of CPLD 124 is completed, IO pin of CPLD 124 is set tological “1” state 312. At this stage analog switch 204 will set switchto state 304 thus connecting TDI line to OUT2, whereas switch 212 willset to state 308 to connect TDO to IN2. This state will be kept forever;CPLD 124 is programmed and is disconnected from the chain of all otherCPLDs (128, 132).

At this stage, any subsequent power up of the board at stage 300 willenable programming of any one of the CPLDs (128, 132) which areconnected in the chain, thus enabling programming of those CPLDs formaintenance reasons in the field. CPLD 124 will not be accessible forprogramming at stage 300 in the field, thus ensuring that the safetyCPLD is not mutative any more.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

PARTS LIST

100 electronic board

104 controller

108 JTAG interface

112 interface lines

124 first CPLD

128 second CPLD

132 last CPLD in chain

200 board before programming of CPLD 124

204 IN lines analog switch

208 switch 204 at OUT1 state: CPLD 124 before programming

212 OUT lines analog switch

216 switch 212 at IN1 state: CPLD 124 before programming

220 program mode line (program done)

224 IO pin at CPLD 124 before programming state

300 board after programming of CPLD 124

304 switch 204 at OUT2 state: CPLD 124 after programming

308 switch 212 at IN2 state: CPLD 124 after programming

312 IO pin at CPLD 124 after programming state

TDI input pin

TDO output pin

TMS timing pin

TCK clock pin

1. An electronic circuit comprising: a plurality of programmablecomponents connected in an electronic chain; an interface adapted toconnect said programmable components to an external controller whereinsaid controller is adapted to program said programmable components; acomponent isolation element connected to said interface at an input endand to said electronic chain of said programmable components at anoutput end wherein said isolation element is adapted to isolate onecomponent of said programmable components from said electronic chain andwherein said one component is a safety component; wherein said componentisolation element comprises: a pull down resistor adapted to force anoutput pin from said safety component to logical state zero at firstpower up of said electronic circuit; a first analog switch adapted tolink an input data line from said JTAG interface to said safetycomponent before programming and to the chain of all the otherprogrammable components after programming of said safety component; anda second analog switch adapted to link an output data line from saidsafety component to said interface before programming and to the chainof all the other programmable components after programming of saidsafety component.
 2. The electronic circuit according to claim 1 whereinsaid interface is a joint test action group (JTAG) interface. 3.(canceled)
 4. The electronic circuit according to claim 1 wherein saidprogrammable component is a CPLD component.